1. Field of the Invention
The present invention relates to an image pickup apparatus, such as a digital camera, which can perform shooting using a light emitting device for irradiating an object, and a method of controlling the image pickup apparatus.
2. Description of the Related Art
Photo shooting includes daylight shooting which is performed under sunlight in the day, so-called strobe shooting which is performed by emitting flashlight toward an object in the dark, and so-called daylight synchro shooting which is performed with a combination of daylight and flashlight. Thus, the photo shooting is performed under various conditions.
As a method of lighting control for strobe shooting, there has been known a pre-flash method. In the pre-flash method, a strobe is preliminarily flashed before exposure for shooting, and an amount of light emission appropriate for actual shooting is calculated by measuring an amount of reflected light from an object obtained by the pre-flash, whereafter a main flash is emitted according to the calculated light emission amount. In this case, in a digital camera having no light metering sensor, an image sensor for image pickup is exposed to reflected light obtained by the pre-flash, and an image signal generated thereby is used for light metering.
In flashing the strobe, a main capacitor is electrically charged in advance, and then in light emission timing, a voltage is applied to a xenon tube while energizing a trigger coil. In doing this, generally, the light emission control is started after the main capacitor is electrically charged to a target charge voltage level (full charge) close to its rated voltage. This is because it is convenient to make constant the amount of preliminary light emission by emitting a pre-flash in a state of the main capacitor charged to the predetermined voltage level and thereby calculate an amount of main light emission to be effected by a main flash based on a photometric value of reflected light obtained by the pre-flash.
However, it takes time to charge the main capacitor to the full, and hence there is a problem that while viewing a scene which requires strobe light illumination, a good moment to take a photo of the scene can be missed. Further, the inflexibility of the charge control method that charges the main capacitor to the full even when only a relatively small light emission amount suffices causes waste of electric power.
To solve these problems, a technique has been proposed in which the main capacitor is charged only by a charge amount enough to obtain a light amount determined on a shooting mode-by-shooting mode basis (see Japanese Patent Laid-Open Publication No. 2006-072049). This proposal asserts that electric power wastefully consumed for strobe shooting can be reduced while maintaining an appropriate amount of light emission adapted to each of various scenes to be shot.
However, the amount of strobe light emission required for shooting is different between different situations of objects at different times, and therefore according to the technique disclosed in Japanese Patent Laid-Open Publication No. 2006-072049, it is difficult to define an appropriate amount of strobe light emission on a shooting mode-by-shooting mode basis.